1. Field of the Invention
The present invention relates to a printing system with a head that can create at least two different types of dots having different hues on an object, so as to record a multi-tone image through a distribution of the dots, as well as to a method of recording images with such a printing system.
2. Description of the Related Art
Color printers, in which a plurality of color inks are discharged from a head, are widely used as an output device of a computer that records multi-color, multi-tone images processed by the computer. There are several techniques available for creating multi-tone images in the process of printing multi-color images with three color inks, cyan, magenta, and yellow (CMY). One available technique, which is adopted in the conventional printers, expresses the tone of a printed image by the density of dots (the frequency of appearance of dots per unit of area) while fixing the size of dots formed on a sheet of paper by a stream of ink droplets. Another available technique adjusts the diameter of dots formed on a sheet of paper, in order to vary the density of dots per unit of area. The advanced fine working of the head for creating ink particles has improved the density of dots formable per predetermined length or the variable range of dot diameters. The improvement in such printers has, however, so far been limited to 300 dpi through 720 dpi in printing density or resolution and several tens microns in particle diameter. This is significantly lower than the level of expression or resolution of silver photography, which has reached several thousands dpi on the film.
Dots are sparsely formed in an area of low image density, that is, in an area of low density of dots to be printed. This increases the degree of granularity and makes the dots undesirably conspicuous. The proposed technique regards the multi-valued process, for example, half-toning process in printers, in order to equalize the frequency of appearance of the respective color dots in the area of low printing density.
Even in the system for equalizing the frequency of appearance of the respective color dots, dots of plural color inks are independently subjected to multi-valued coding and formed in the process of multi-color printing. In some cases, this causes uneven distribution of cyan dots and magenta dots, thereby making the granularity undesirably conspicuous.